X-ray generator target construction



May 27, 1958 2. J. ATLEE X-RAY GENERATOR TARGET CONSTRUCTION Filed Feb.11, 1957 INVENTOR. ZED J. ATLEE A T TORNEY5 2,836,757 Patented May 27,1958 X-RAY GENERATOR TARGET CONSTRUCTION Zed J. Atlee, Chicago, 111.,assignor to Dunlee Corp., Chicago, Ill., a corporation of IllinoisApplication February 11, 1957, Serial No. 639,350

Claims. (Cl. 313-330) The present invention relates to X-ray generatorsand more particularly to a new and improved anode structure for X-raygenerators.

In making a radiograph wherein X-rays are generated by exciting an X-rayemissive element, generally termed a target element, with a beam ofelectrons, the object being radiographed is positioned between thesource of X- rays and an X-ray sensitive medium so as to secure a shadowpicture of the object. Obviously, the best definition in the picturewould be obtained with a point source of X-rays. However, because of theheat generated by the impingement of electrons upon a target element, itis the practice to distribute the electrons over a relatively elongaterectangular area of the target and to tilt the target relative to theobject being X-rayed so as to foreshorten the target area and, ineffect, concentrate the X-ray source area. This is known as theline-focus principle.

To X-ray an object of relatively large area requires a source of greaterintensity than is necessary for objects of lesser area, and, so thatoverloading of the target element does not occur, it is necessary inproviding sources of relatively greater intensity to distribute theexciting electrons over a larger area than is required for formingsources of lesser intensity.

Now, many users of an X-ray generator have occasion for using X-raysources of large intensity and other occasions for using a source ofsmaller intensity and of smaller effective area so as to secure shadowgraphs of greater definition. To accommodate this dual demand, so-calleddouble focus generators such as shown in my prior Patent No. 2,767,341have been provided. The double focus generators provided heretofore havea pair of electron generating means capable of forming rectangulartarget areas of different size upon different portions of an anodetarget. Heretofore the target inclination to obtain the line-focuseffect mentioned above has been the same for both portions of the targetwith the result that full utilization of the value of the linefocusprinciple has not been realized.

it is, therefore, an object of the present invention to provide a newand improved double focus X-ray generator.

A more particular object of the invention is to provide a new andimproved X-ray generator anode.

A specific object of the invention is to provide an X- ray generatorhaving means for providing a source of X-rays of relatively highintensity and further means for providing a source of lower intensityand concentrated area so that the generator may be used as desired forX-raying objects of relatively large thickness or area or alternativelyfor X-raying thinner objects or smaller areas with better definition.

Other objects and advantages will become more apparent hereinafter.

In accordance with the illustrated embodiment of the invention, I haveprovided an X-ray generator having a cathode unit including means forgenerating a pair of electron beams of rectangular cross section, Thebeams are focussed upon an anode target element having separate targetportions for each beam. Both target portions are tilted so as toforeshorten the target area relative to an object being X-rayed, thetarget portion for the smaller beam being tilted so as to obtain arelatively greater foreshortening of the target area, thus providing asmall, concentrated focal spot.

For a more detailed description of the invention, reference is made tothe accompanying drawings wherein:

Fig. l is a side elevational view of an X-ray generator made inaccordance with the invention;

Fig. 2 is a fragmentary view looking in the direction of the arrows 2-2of Fig. 1;

Fig. 3 is an end View of the cathode of the generator, looking in thedirection of the arrows 3-3 of Fig. 2;

Fig. 4 is an end view of the anode looking in the direction of thearrows 4-4 of Fig. 2;

Fig. 5 is a fragmentary, sectional view taken generally along line 55 ofFig. 1;

Fig. 6 is a sectional view of the anode taken along the line 6-6 of Fig.4;

Fig. 7 is a sectional view of the anode taken along line 7-7 of Fig. 4;

Fig. 8 is a sectional view of the anode taken substantially along line88 of Fig. 1; and

Fig. 9 is an enlarged, perspective view of the anode target elementremoved from the anode body. I

The present invention is illustrated in'connection with an X-raygenerator comprising an envelope 10 of glass or other suitable material,a cathode unit 12 suitably mounted in one end of the envelope and acoaxial anode unit 14 suitably mounted in the other end of the envelope.The envelope 1% may be provided with a window portion 15 for theemission of X-rays.

Referring particularly to Fig. 3, the cathode unit 12 is preferablyformed with two plane faces 16, 18 facing the adjacent end of the anodeunit 14. The faces 16, it; are disposed at a large obtuse angle withrespect to one another and intersect along a line 19 perpendicular tothe longitudinal axis of the cathode head. .Formed in the face 16 is anelongated focussing cup recess 20 in which is mounted an elongatedfilament 22 for generating and focussing upon the anode face arectangular electron beam 23. Formed in the face 18 isa smaller electronfocussing cup 24 in which is mounted a shorter filament 26 forgenerating and focussing upon the facing end of the anode a rectangularelectron beam 27 of smaller dimensions than the electron beam 23, aswill be explained in greater detail hereinafter. The electron beams 23,27 are focussed upon the anode with their longer cross sectional axes,indicated in Fig. 4 at 29, 31, respectively, substantially parallel. Thefilaments 22, 2e are connected to suitable leads indicated at 28 forconnecting the filaments to a source of energy. 7

The anode unit 14 comprises a body 17 preferably formed of a metalrelatively high heatconductivity such as copper. The end of the anodefacing the cathode unit 12 is recessed or indented and embedded thereinis a unitary re-entrant target element of tungsten or other metal ofhigh atomic number formed with two planar face portions 32, 34 definingseparate target areas for the electron beams 23, 27, respectively. Aunitary rather than a two piece target element is preferred since in thecase of a two piece target element the small strip of copper between theembedded pieces tends to overheat and penetrate or overfiow the edges ofthe target pieces, destroying their utility. Viewing the anode end asshown in Fig. 4, the electron beam 23 impinges on the target portion 32over a rectangular area or focal spot 36 whereas the beam 27 impinges onthe target portime 34 eve; a smallerrectan picture obtained,

'4 ar area or' focal spot 38.

Referring-particularly to-Eigseland-5, ina self-rectifying generator theface. portions .-;32,,34 of the target element 7 are preferably inclinedat an angle A towards each other relativetoa plane perpendi'cnlarto theaxis of the anode,

as -indicatedih Fig, 5, and -for the reasons set forthin my, p'riorPatent No. 2,767,341 The angle A may-be, for'example, '20 degrees, butitis to be understood that the {degree ofrinclinationis not critical andmay be varied. It will be furthertunderjstood that in the case ofgenerators-operated with direct current, the face portions 32,34 neednot be inclined toward each other.

*-;In addition to 'being inclined toward one anotherythe target portions32, 34 are each inclined at an acute angle with-respect to the crosssectional axis of the beam focussed thereon, ;and,-in accordance withthe invention,

the a'ngles of incl-ination'of the target faces with respect to the beamfocu ssed thereon are different from 'one another Inf the illustratedembodiment of the invention, the target portion 32 upon which theelectron beam -23 is focussed isinclined'at an angle of 73 degrees withrespect to the beam axis 29,-or at'an angle of 17 degrees with respectto aplane normalto the axis of the anode unit, as indicated in Fig. 7;As c omparedrto this, the

targetportion 34 is'inclined at an angle of 78 degrees 7 with respect tothe axis 31 of the electron beam 27, or

at angle of 12 degrees with respect to a plane normal to the axis of theanode unit as indicated in Fig-6;

These angles-are, of course, tobe taken as merely illustrative and it istobe understood'that the angles of inclination may be varied to meet'theconditions desired. To better illustrate the relation of the targetportions velope axis and substantially parallel to the direction of thecathodefilamentsyand through the envelope window l5. Thus, viewed fromthe object being photographed, the target areas 36, 38 are eachforeshortened, as shown in-Fig. 2, to a small, nearly square, rhombus.

It will be appreciated that, though as mentioned before apoint source istheoretically the ideal, a square or nearly square source'of X-rays isthe preferred practical configuration'in an X-ray generator of the classdescribed so as to 'obtain the best. possible definitionin the shadow,Itwill also be apparent that to X-ray a large area ,will require moreX-raysthan would be required to X-ray a'smaller area. 'While a singlesource may be utilized to X-ray Iarge and small areas by varying thetotal time of exposure, this is not desirable for various reasons which.

need not be. mentioned here. Instead it is preferred to provide ardoublefocus generator such as shown in'my prior Patent No. 2,767,341,mentioned previously, which maybe operated to provide a small source ofX-rays capable of generating a given number. of X-rays per unit of timefor X-raying a small area, or to provide a larger of the target werethen established. This generallyjre sulted-in-providing--an angle oftilt on -thetargetof-be-' tween about 17' degrees to 20 degrees. I

Next the shape of the smaller target area was considered. With thedesired intensity of the smaller source established, the necessary shapeof the target area to obtain the smallest possible square, i. .e.,rhombic, projection was determined. "'A principal advantage of, thepresent invention arises at this point, for with the steeper angle oftilt provided in a generator of the invention, the target'area for thesmall focal spot can be so shaped as to produce a smallerprojectioncapable of producing the same number of X-rays as compared to the sizeof the projection of the smaller target areas which could, be secured inthe generator construction heretofore employed. This is becausethesteeper. positioning of the target portion 32 results in greaterforeshortening of the projection of the focal spot toward the objectbeing. X

rayed. a consequence, the focal spot38 may" be made relatively narrowerthan could be done in thecase of generators as designed heretofore.Therefore, it"is.

possible with thegenerator of the invention to secure-X-ray'shadow"graphs, with better detail becausefofthe V smaller-sizeof-the'focal spot 38. j i "This-is'of extreme value, for example, toradiologists making X-ray examinations of parts of thetbod y. "Inmakingthe initial exploratory examinations, the genershadow graph of the areain question with greater detail.

Similar advantages accrue to other. users of the invention.

Having illustrated and described a preferred embodiment ofthe invention,it should be apparent to those skilled in the art that theinventionpermits of modification in arrangementand detail. I claim, asmy invention all such modifications as come within the true spirit andscope of the appended 'claims.

I claim:' r

1. An X-ray generator comprising cooperating anode and cathode unitsfacing each other in spaced apart relation, said cathode unit having apair of laterally spaced apart electron generating means for generatingand focussing a pair of substantially parallel beams of electrons uponthe facing end of said anode unit with said beams each having arectangular cross section but being of differentcross sectional lengthwith the longercross sectional axes of the beams substantially parallelto one another, said anode unit having a unitary target element isfocus'sed being inclined at an angle of about 12 degrees with respect tothe longer cross sectional axis of the beam focussed thereon, the otherof said face portions being inclined at an angle of about 17 degreeswith respect to source capable of generating a larger number of .X-raysfor the same unit of time for X-raying larger areas and also capable ofgenerating more intense X-rays for X-ray- 7 ing thicker bodies.

. The double'focus generators provided heretofore have had the sameangle of tilt provided for the target portions for both the large andthe small focal spot, but the angle of tilt has; been largelydetermined'by the requirement to-get a square projection of the largefocal spot. Indesigning the generator/the intensity desired for thelarger source was first decided. Having decided the intensity of thesource, the most ideal angle of tilt and theshape of thetarget area toobtain the. smallest possible .square .projectignlwithfthe..maximurrrsafe loading the longer cross sectional axis of the beam focussedthereon a i 2. An X-ray generator comprising cooperating anode andcathode units facing each other in spaced apart relation, said cathodeunit having a pair of laterally spaced apart electron generating meansfor generating and tron bearns, one of said face portions being inclinedat an angleof about 12 degrees with respect to the longer crosssectional axis of the beam focussed thereon, the other of saidfaceportions being inclined 'at an angle of abont 17 degrees withrespect to the longer cross sectional axis of the beam focussed thereon.

3. An X-ray generator comprising cooperating'anode and cathode unitsfacing each other in spaced apart relation, said cathode unit having apair of laterally spaced apart electron generating means for generatingand focussing a pair of substantially parallel beams of electrons uponthe facing end of said anode unit with said beams each having arectangular cross section and with the longer cross sectional axes ofthe beams substantially parallel to one another, said anode unit havinga unitary target element having two planar face portions each definingseparate target areas for each of said electron beams, each of said faceportions being inclined at an acute angle with respect to the longercross sectional axis of the beam focussed thereon, the angle ofinclination of said face portions being different from one another.

4. An X-ray generator comprising cooperating anode and cathode unitsfacing each other in spaced apart relation, said cathode unit having apair of laterally spaced apart electron generating means for generatingand focus sing a pair of substantially parallel beams of electrons uponthe facing end of said anode unit, with said beams each having arectangular cross section but being of different cross sectionallengths, said anode unit having two planar faced target element portionseach defining a separate target area for one of said electron beams,said face portions being inclined at small acute angles with respect tothe longer cross sectional axis of the beams focussed thereon, the faceportion upon which the beam of the smaller cross sectional length isfocussed being inclined at a steeper angle relative to the crosssectional axis of said beam than the angle of inclination of the otherface portion relative to the cross sectional axis of the beam focussedthereon.

5. An X-ray generator comprising cooperating anode and cathode unitsfacing each other in spaced apart relation, said cathode unit having apair of laterally spaced apart electron generating means for generatingand focussing a pair of substantially parallel beams of electrons uponthe 'facing end of said anode unit, with said beams each having arectangular cross section, said anode unit having a unitary targetelement having two planar faced portions each defining a separate targetarea for one of said electron beams, each of said face portions beinginclined at a small acute angle with respect to the longer crosssectional axis of the beam focussed thereon, the angles of inclinationof the face portions relative to the corresponding cross sectional axisdiifering on the order of 5 degrees.

References (Iited in the file of this patent UNITED STATES PATENTS2,767,341 Atlee Oct. 16, 1956

